The invention relates to a cooling apparatus for a high pressure, lubricant-flooded thrust bearing and, more particularly, relates to a system for continuously forcing a high volume of liquid coolant between the thrust pads and an associated runner bearing surface to cool the pads and runner sufficiently to enable them to effectively support a substantially heavier load, without damage to the bearing, than would otherwise be possible in the absence of the cooling system.
It has long been recognized that the load bearing capabilities of thrust bearings can be increased by maintaining the bearing surfaces at sufficiently low temperatures to prevent the metal of those surfaces from being softened sufficiently to cause wiping of the bearing. In addition to developing various systems for cooling the lubricant used to enable the bearing surfaces of thrust bearings to slide smoothly relative to one another, different types of thrust pad geometries have been developed to help control the load distribution and flow of lubricant between individual thrust pads of given bearings and their associated runner surfaces. In general, thrust bearings for supporting vertical loads are presently designed to use either a plurality of pivotally supported thrust pads in conjunction with a suitable thrust bearing runner surface, or are made to include a plurality of relatively more flexible thrust pads that are supported over most of their area by a set of compression springs in a manner such that the individual pads can flex or bend slightly relative to the substantially flat bearing surface of an associated runner bearing, to enable a predetermined amount of lubricant to be swept between the pads and the runner by rotation of the bearing surfaces relative to one another, in a generally well known manner.
In recent years, the unit-area loading of vertical thrust bearings has increased dramatically in the field of hydroelectric generation, because larger and larger rotor assemblies have been mounted in generators that afford very limited space to accommodate a thrust bearing assembly and any associated bearing cooling apparatus. Many of the prior art thrust bearing systems that were examined, in an attempt to discover a satisfactory solution to this problem of increasing bearing loadings restricted by relatively fixed confining limits on space available for the bearing system, reveal some structural features that are similar to some of the features of the invention disclosed herein. However, insofar as the applicant can ascertain, no prior art thrust bearing systems use the novel combination of structural features he employs to achieve the optimum bearing cooling function provided by his invention.
An example of a forced-feed lubrication system for a pivoted-shoe type of thrust bearing is disclosed in U.S. Pat. No. 3,004,804--Pinkus, et al. which issued on Oct. 17, 1961 and is assigned to the assignee of the present invention. A thrust bearing utilizing spring assemblies to support its individual thrust pads is disclosed, for example, in U.S. Pat. No. 4,168,101--DiGrande, which issued on Sept. 12, 1979 and is also assigned to the assignee of the present invention. The bearing cooling system disclosed in the Pinkus patent appears to be intended for use primarily with journal bearings, rather than with heavily loaded vertical thrust bearings of the type for which the present invention is particularly useful. Moreover, as explained in the specification of the Pinkus patent, the larger portion of lubricant entering between the respective bearing pads and an associated journal bearing surface is designed to enter the leading edges of the respective pivoted bearing pads thereby to furnish a supply of cool oil for formation of the normal wedge-shaped oil film upon which the shaft is intended to ride. At the same time a smaller portion of lubricant is introduced at the trailing edge of the respective pivoted bearing pads to act primarily as a cooling agent. Thus, it appears that the purpose of the Pinkus system is to cool lubricant as it is about to leave the respective bearing pads so that heat is not accumulated and transmitted from one pad to another.
In a somewhat related cooling system described in U.S. Pat. No. 3,339,990--Wendt, which issued July 13, 1964, there is disclosed a pivoted-block thrust bearing system for a shaft, in which system a lubricant supply passage to the respective thrust blocks of the bearing is provided generally parallel to the axis of the shaft. That system is designed to overcome one of the disadvantages of earlier systems that are designed to supply lubricant to pivoted thrust bearing blocks or pads. By positioning a lubricant inlet in the respective bearing blocks at a location thereon which remains in a substantially constant spatial relation to a supported shaft, the risk of breakdown in the supplied lubricant film of the system is somewhat diminished.
In other types of bearing systems, high pressure lubricant is used primarily to support a load on a hydrostatic film that is maintained under a predetermined pressure by forcing lubricant between selected bearing surfaces. An example of such a hydrostatic bearing system is shown in U.S. Pat. No. 3,545,824--Korrenn, which issued on Dec. 8, 1970. The high pressure lubricant forced into such bearings is intended primarily to form a load supporting surface, rather than being designed to assure appropriate cooling of the bearings; thus, the lubricant is forced into recesses defined in opposite surfaces of bearing blocks, near the center of those surfaces, rather than being introduced to thrust bearing pads in the manner used for the coolant in the invention disclosed herein.
In yet another prior art thrust bearing lubrication system, as disclosed in U.S. Pat. No. 3,784,266--Parlevliet, which issued Jan. 8, 1974, a high pressure pump is used to selectively control the flow of lubricant into grooves formed in the respective leading and trailing edges of each of the thrust pads of a thrust bearing. The flow of oil into these grooves is controlled to provide a means for altering the region of the thrust pads over which the bearing-lubricating film is developed. By thus controlling the lubrication film, the pivoting motion of the respective pads can be controlled in a desired manner, similar to the type of control that could be attained by varying the location of the pivot points for the respective thrust pads.
A common type of alternative thrust bearing cooling arrangement is generally similar in function to that described in the above noted patent to Pinkus, in the lubricant flowing between the respective thrust pads and runner bearing surfaces is cooled as it leaves each pad so that heat is not carried from one pad to an adjacent pad. An example of a prior art structure disclosing such a system is shown in U.S. Pat. No. 3,905,657--Ishida, which issued Sept. 16, 1975. In that system, a relatively low pressure supply of oil is injected into chambers, each of which respectively surround the different thrust pads of the bearing. Primary lubrication for the bearing is provided by flooding the bearing surfaces in a well known manner, but the low pressure lubricant introduced into the chambers surrounding the thrust pads operates to cool lubricant that is heated by its passage between the respective thrust pads and the bearing runner. A somewhat similar system is disclosed in U.S. Pat. No. 3,454,312--Bielec, which issued July 8, 1969. In that system, a plurality of spray heads are positioned between adjacent thrust pads of a thrust bearing. The spray heads operate to force cooling oil into the flow of lubricant that is carried from one thrust pad to another thereby to cool the lubricant between the respective thrust pads. In such common prior art systems, no high pressure coolant is forced directly between the thrust pads in the manner disclosed hereinafter relative to the present invention.
Other prior art patents disclose a variety of configurations of grooves and associated supply channels in thrust bearing pads to provide various lubricating functions. For example, U.S. Pat. No. 3,982,796--Hill, which issued Sept. 28, 1976 discloses a thrust bearing having thrust pads that are provided with a pair of grooves spaced respectively from the leading and trailing edge of each pad and are connected to oil supply conduits that are operable to selectively drain oil from a load bearing film between the thrust pads and the associated bearing runner thereby to provide a desired pressurized oil support for the respective thrust pads in lieu of a pivotal or multiple-spring support system. In general, the disclosure of Hill, thus, appears to be directed toward the type of function discussed above relative to the Parlevliet U.S. Pat. No. 3,784,266. Another U.S. Pat. No. 3,549,215--Hollingsworth, which issued Dec. 22, 1970 discloses a thrust pad system having grooves in the surfaces of thrust pads and associated conduits for supplying lubricant to the grooves. The system is operable to selectively bleed lubricant from the load supporting film in the manner generally discussed in the above-noted Hill patent. The primary purpose of such systems is to supply lubricating oil in controlled volume to the bearing surfaces, rather than to provide a cooling function for the bearing.
In addition to such lubricant supply and control systems, which are generally well known in the prior art, it is also a common practice to provide means for introducing high pressure lubricant between thrust pads and an associated runner bearing surface in order to lift a thrust bearing runner to initially start rotation of the runner relative to the pads. High pressure lubricant systems for performing such lifting functions to start rotation of a supported load are not designed to provide a continuous, relatively high volume of coolant between the bearing surfaces when the bearing operates at its normal speed. An example of a system that might be usable to perform such a lifting function is disclosed in U.S. Pat. No. 3,625,576--Miller, which describes a system of passageways formed in the bearing surfaces of a thrust bearing to deliver oil to supply grooves in the generally flat face of the bearing surface to form a lubricating film between that surface and a juxtaposed bearing surface.
Finally, it is known in the prior art to provide thrust bearing pads with grooves adjacent their respective leading and trailing edges coupled to oil supply conduit systems that are operable to selectively force a flow of lubricant to either of the grooves in the respective pads thereby to assure a predetermined supply of low pressure lubricating oil to the leading edge of each pad, regardless of the direction of rotation of an associated shaft or runner bearing surface. An example of such a system is disclosed in U.S. Pat. No. 3,891,281--Jenness, which issued June 24, 1975. Such systems are intended primarily to supply sufficient lubricant to form a lubricating film between the bearing surfaces, but are not designed to provide a relatively large flow of coolant between the bearing surfaces to cool them sufficiently to enable relatively heavy loads to be continuously supported on the thrust bearing pads in the manner of the invention disclosed herein.
While it is apparent from an examination of prior art bearing lubricating systems, such as those described in the foregoing patents, that it is common to design thrust bearing pads with a variety of groove patterns in their respective bearing surfaces and to couple lubricant supply systems to those grooves in order to selectively control the flow of lubricant to the bearing surfaces, for the various purposes noted above in the individual patents, there appears to have been little progress made in directly cooling the bearing surfaces of the individual thrust pads of such arrangements. Although the above noted Pinkus patent describes a thrust bearing system that utilizes a plurality of pivoted thrust pads having cooling oil introduced near the trailing edge of each of the respective pads to prevent heat from being carried by lubricant from one pad to the next pad, no prior art thrust bearing system known to the present applicant provides relatively flexible, spring supported thrust pads with distributing grooves and associated conduit supply means for introducing a large volume of high pressure coolant between the thrust pads and an associated runner bearing surface to cool a major portion of each of the thrust pads.
An object of the present invention is to provide a thrust bearing cooling apparatus that enables such bearings to be loaded to heretofore unattainable high levels per unit area while protecting the babbit metal surfaces of the bearings from damange due to excessive heating and resultant excessive wear or "wiping."
Another object of the present invention is to provide a flooded-type thrust bearing with flexible, spring-supported thrust pads that include coolant distributing grooves in the bearing face of each pad and associated conduit means that are operable to introduce a large volume of high pressure coolant between the thrust pad bearing surfaces and an adjacent bearing surface of a runner, thereby to cool substantially the entire working surfaces of the bearings, and to cool the flow of lubricant that is drawn between the bearing surfaces by normal relative rotation of those surfaces.
A further fundamental objective of the present invention is to provide a maximum temperature reduction of the bearing surfaces of a thrust bearing, while utilizing the least pumping power and smallest pump size possible to force coolant between the bearing surfaces to achieve such an optimum desired temperature reduction.
Still another object of the invention is to provide a thrust bearing cooling apparatus that is equally effective independent of the direction of rotation of a supported load on the bearing.
A still further object of the invention is to provide a thrust bearing cooling apparatus that is operable to pump liquid coolant into spaced grooves adjacent both the leading and trailing edges of each thrust pad of a bearing. The system operates to pump a larger volume of coolant into the distributing groove on the leading edge of each bearing pad than is pumped into the distributing groove adjacent the trailing edges of the thrust pads, thereby to optimize the cooling benefit afforded by the system.
Yet another object of the invention is to provide a thrust bearing cooling apparatus in which high pressure coolant is forced between spring supported, relatively flexible thrust pads and an associated runner bearing surface in a volume that is in the range of one-third to one-half the total flow rate of lubricant that is swept between those surfaces from a pool of liquid in which the thrust bearing is normally operated.
Further objects and advantages of the invention will become apparent to those skilled in the art from the description of it herein presented in connection with the accompanying drawings.